Thermostat with expansion neutralizer



1957 E. G. FRANKLIN THERMOSTAT WITH EXPANSION NEUTRALIZER Filed April 22, 1954 IN V ENTOR. 6. E m/W form/v0 United States Patent IHERMOSTAT WITH EXPANSIGN NEUTRALIZER Edmond G. Franklin, Minneapolis, Minn assigaor to General Mills, Inc, a corporation of Delaware Application April 22, 1954, Serial No. 424,303 Claims. (Cl. 200-437) This invention relates in general to electrically heated appliances and pertains more particularly to a temperature control therefor in which the expansion of the heated member serves as the means for obtaining the temperature measurement or response.

While the instant invention is directed to subject matter possessing utility when used with a variety of electrically heated appliances, it has especial utility when employed in conjunction with an electric flatiron where the expansion and contraction of the iron soleplate is instrumental in controlling the energization of the heating element. However, utilizing the actual expansion of the electrically heated member, the soleplate in the case of the abovealluded to iron, carries with it certain attendant disadvantages or problems.

First of all, the electrically heated member or soleplate, for high accuracy of control, must be in relation to another member, the difference in expansion between the two members providing the actuating force for the switch contacts of the thermostat. Since the second or reference member will not have a zero coefficient of expansion and will be influenced by heat transferred from the first member, errors will creep into the regulation, which errors are dependent upon the particular temperature of the reference member at any given time.

What may be termed expansion neutralizers" have been employed, one type of neutralizer involving the utilization of two bars having different degrees of thermal expansion and a lever connecting between said bars so that the expansion is, as the name implies, actually neutralized. Such an arrangement thereof requires that the spacing of the fulcrum points on the lever be quite critical as to proper lengths therebetween.

Accordingly, one important object or" the present invention is to provide a very simple thermo-static arrangement, yet at the same time avoiding the rather critical spacing requirements demanded from the prior art arrangement mentioned above.

Also it is an aim of the invention to provide a thermostatic arrangement that is compact, particularly in a vertical direction where space, especially in the case of a llatiron, is important as far as minimizing bulkiness and weight is concerned.

Another object of. the invention is to utilize inexpensive materials in the construction of the thermostat so that the over-all cost of the appliance may be kept at a low figure. More specifically, it is within the contemplated invention to avoid having to use materials possessing exceptionally low COEZH'lClCIllS of expansion, which materials are normally quite costly;

A still further object of the invention resides in the desideratum that the thermostat be accurate in its operaice 2 tion. This object is inherent in the structure forming the subject matter of the instant invention.

Other objects will be in part obvious and in part pointed out more in detail hereinafter.

The invention accordingly consists in the features of construction, combination of elements and arrangement of arts ahich will be exemplified in the construction hereali'ter set forth and the scope of the application of which will be indicated in the appended claims.

in the drawing:

Figure l is a perspective view showing sufficient fiatiron structure with which to illustrate the salient features of the invention;

Figure 2 is a sectional view taken in the direction 05 line 2-4. of Figure l, and

Figure 3 is a perspective detail showing the switch contacts and the mounting and adjusting structure associated therewith.

To simplify the drawing as much as possible, only sutlicicnt structure is presented therein which is deemed necessary to illustrate the features of the invention. Therefore such details as the handle and casing for the Flatiron, selected as the particular electrically heated appliance in connection with which the invention will find usefulness, have been omitted.

Referring now in detail to the drawing, it will be observed that the electric fiatiron comprises a soleplate 10 having embedded therein a conventional electric heating element 12, the ends of which are exposed and have been designated by the numerals 1d and 16. For the purpose of energizing the heating element 12 there is provided a switch structure designated generally by the numeral 18. This switch structure includes a base member 20 having an upstanding integral ear 2 which serves as the means for supporting an inverted U-shaped bracket 24, the bracket being fixedly connected to the ear, such as by a rivet 2d. the base member 29 is secured to the soleplate 10 by reason of a pair of screws 28.

Between the vertical legs of the U-shaped bracket 24 is carried a pair of resilient switch arms 30 and 32, each of which is equipped at its free end with a contact 34, 36. A plurality of insulating washers 38 serves to insulate the switch arms 3:; and 32 from each other. Also placed between the vertical legs of the bracket 24 is a pair of terminal elements id and -32, these elements being in respective electrical contact with the switch arms 30 and 32. Holding the switch arms, the insulating washers, and the terminals in stacked relation is the previously alluded to rivet 25. For the purpose or" obtaining the temperature range in which the contacts 34 and 36 open and close, the base member 20 is equipped with an upstanding section 4-6 merging into a horizontal flange 48. The horizontal flange journals adjusting shaft 50, having at its upper end a manipulating knob 52 and carrying at its lower end an involute cam 54. The switch arms 30 and 32 are normally biased apart, but engagement of the cam 54 against one side of the arm 32 is instrumental in overcoming the bias of said switch arms, the particularly rotata-ble position of the cam determining to what extent such bias is overcome.

Connecting the end 14 with the terminal 42 is an insulated conductor 56. A similar conductor 58 leads from the terminal 40 and is intended to be connected to one side of a source of electric power such as by way of a flexible cord (not shown). The other side of the source of electric power is intended to be connected via thementioned cord to the end 16 of the heating element 12. Thus it will be seen that the contacts 34 and 36 are in a serial relation with the heating element 12 and opening or closing of the contacts will be responsible for energizing the heating element when the con actor 58 and the end l6 are connected to the above-alluded to power source.

Up to this point, the structure described is, in its general attributes, old and well known. The mechanism for actuating the contacts 34 and 36 will now be explained, this mechanism being novel, it is believed.

To this end the invention envisages the employment of three strips or bars 60, 62, 64 disposed in parallel relation with each other. One end of the bar 66 is fixedly anchored to the soleplate 10 by reason of an integral upturned car 65 which is attached to one flange of an angular member 66 such as by a rivet 67. The angular member 66 is in turn fastened to the soleplate by means of a pair of screws 68. The other end of the bar 69 is fixedly connected with the tapering or adjacent end of the intermediate bar 62, such connection being by way of a transverse strip 70 and a plurality of rivets '72, two to each bar. Similarly connecting the opposite end of the bar 62 to the neighboring end of the bar 64 is a second transverse strip 7 S and a second plurality of rivets 89. The other end of the bar 6 is upturned at 32 to provide a vertical flange.

This vertical flange threadedly carries a calibration screw 84 which abuts against a confronting section 86 of an angular member 83 which is secured to one side of the switch arm 30 as by means of a pair of rivets 90. v

in the illustrated embodiment, each of the bars or strips 62' 62, and 64 is of approximately the same length. When the bars are of the same length, the coefdcient of thermal expansion of the bar 62 should be substantially twice that of either the bar 60 or 64. Assuming that such condition prevails, then if the bar 60 expands, say mils to the right as viewed in Figure t, then the bar 62 which will expand a total of 10 mils will expand a net of 5 mils to the left, for 5 mils of the l0 mil expansion of the bar 62 will be utilized to counteract the expansion of the bar 66. Thus, up to this particular point, the bar 62 will, under these assumed conditions, expand 5 mils to the left. However, since the bar 64 has the same coefficient of expansion as the bar 60, it will, under these conditions, expand 5 mils to the right, thus totally neutralizing the expansion that has taken place throughout the three bars 60, 62, and 64.

Inasmuch as the base member is fixedly mounted to the soleplate it), the expansion of the soleplate will cause the base member 24 to move relative to the angular member 64. Thus the anchored end of the bar 69 may be considered as a reference or datum point and the fixed position of the base member as a second reference or datum point. The end 82 of the bar 64, as has already been said, will not move relative to the anchored end of the bar 6% However, since the bar 29 is fixedly disposed on the soleplate 10, the switch structure including the contact arms 30 and 32 will move toward the right when viewed in Figure 1. Movement of the arm 30 causes a force to be applied by the screw 84 against the section 36 of the angular member 88, for the screw 84 remains immobile and the section 36 is carried along with the base 29 in its relative movement with respect to the angular member 64. This force produced between the screw 86 and the section 86 is instrumental in causing the switch arm 39 to pivot or fulcrum about its fixed end which is intermediate the vertical legs of the U-shaped bracket Suificient movement will result in the switch contact 34 becoming separated from the contact 36. By means of the cam 54 and the adjusting knob 52 it will be readily recognized that the particular temperature of the soleplate at which this contact separation occurs can be adjustably obtained for the particular temperature desired.

Once the contacts'34 and 36 have become separated,

the heating element 12 is immediately deenergized and,

the soleplate begins to cool and contract. After sufficient contraction, the contacts 34 and 36 will again come together and the heating element 12 will be energized once more. This action repeats itself and causes a cyclic energization and deenergization of the heating element to maintain the temperature of the soleplate 10 within a preselected range.

While in the described embodiment the bars 60, 62, and 64 have been depicted as having approximately the same length and a one to two ratio between the coefiicient of expansion of the bars 60 and 64- as compared with the bar 62, nonetheless it will be fully appreciated that if the expansion ratio is not actually one to two then compensation therefore can be made by lengthening or sncirtening one of the bars, say the bar 64.

By reason of the afore-described structure including the bars 6 3, 62, and 64, it will be observed thatit is only the expansion of the soleplate 10 that affects the operation of the contacts 34 and 36, for each of the bars 60, 62, and 64 will be subjected to the same temperature conditions since it is contemplated that they will be in a proximal relationship with each other. It is of no consequence that the bars 60, 62, and 64 expand and contract due to heat transferred from the soleplate for their respective expansion and contractions will always be neutralized as described above.

As many changes could be made in the above construction and many apparently widely different embodiments of the invention could be madewithout departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

it is also to be understood that the language used in the following claims is intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

I claim:

1. in a thermostatic switch for an electrically heated appliance, first, second, and third longitudinally, thermally expansible elements disposed in parallel relation with one end of the first element being fixedly connected to the adjacent end of the second element and with the opposite end of said second element being fixedly connected to the adjacent end of said third element, said opposite end of the second element being free to move relative to the other end of the first element and the other end of the third element being free to move relative to said adjacent end of the second element, and said first and third elements being capable of substantially the same amount of lengthwise expansion for a given temperature increase and said second element being capable of approximately .twice the lengthwise expansion of the first or third element.

2. The combination set forth in claim 1 in which the three elements are approximately the same length with the second element having substantially twice the coefficient of expansion as the first and third elements.

3. in combination with an electrically heated member, a thermostatic switch comprising first, second and third longitudinal, thermally expansible elements disposed in parallel relation on said member, with the first end of each element pointing in one general direction and the second end of each element pointing in the opposite direction, means anchoring the first end of the first element to said member, means anchoring the second end of the first element to the second end of said second element, means anchoring the first end of the second element to the first end of the third element, the first end of said second element being free to move relative to the first end of said first element and the second end of said third element being free to move relative to the second end of 5. The combination set forth in claim 4 in which the three elements are approximately the same length with the second element having substantially twice the coefficient of expansion as the first and third elements.

References Cited in the file of this patent UNITED STATES PATENTS 1,795,400 Jones Mar. 10, 1931 10 2,204,791 Davis June 18, 1940 2,660,646 Fritzinger Nov. 24, 1953 

